Setting Up IoC in ASP.NET MVC using Castle Windsor

Abstract: This post gathers information needed to setting up Inversion of Control (IoC) in an ASP.NET MVC application using Castle Windsor.

Introduction: In previous post I summarized how ASP.NET MVC components work together to process request from user and return result . In that post I mentioned we can customize each step to satisfy our needs so I’m going to show you how you can create a custom Controller Factory to implement IoC in your application. For more information about IoC and why we use it you can take a look at this like :http://www.mikesdotnetting.com/Article/117/Dependency-Injection-and-Inversion-of-Control-with-ASP.NET-MVC .

I learned how to use Windsor to set up IoC by reading the great book of Steven Sanderson “Pro ASP.NET MVC framework”. You can read the section I used for this post here :Pro ASP.NET MVC framework by Steven Sanderson

You can get the latest version of Castle project here : www.castleproject.org/castle/download.html

After download and install Castle Project follow these steps to set up IoC in a very simple MVC project. I use default project template & routing configuration that comes with MVC 2.

1.Right click your References folder and add reference to “Castle.Core.dll”, “Castle.MicroKernel.dll”, “Castle.Windsor.dll” files which are in  “C:\Program Files\CastleProject\Bin\net-2.0 after installing Castle.

2.Next we are going to create a custom Controller Factory class. Add WindsorControllerFactory.cs to the root of your application and write these lines of codes to create a controller factory which uses castle to load the required objects at run time base on configuration section which we set up later. Don’t afraid of XML & Reflection parts in the code. These snippets just say to Windsor Container that where in the Web.config file look for registering components and Reflection part just registers all controllers’ types as components. Usually when we use IoC we want to inject an object to an constructor parameter at run time, but in constructor code we just say which interface that object implements but IoC Container loads the needed object base on its configuration. The Interfaces, objects and classes which their constructor injected are components of an IoC container. In this example we register components in two places: We register controllers in the controller factory but register other types using  castle section in Web.config file. So let just right the needed Controller Factory which uses the snippets of Steven’s book that I just updated it to be compatible with MVC 2:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using Castle.Windsor;
using Castle.Windsor.Configuration.Interpreters;
using Castle.Core.Resource;
using System.Reflection;
using Castle.Core;
using System.Web.Routing;

namespace Mvc2Application6
{
    public class WindsorControllerFactory : DefaultControllerFactory
    {
        WindsorContainer container;
        // The constructor:
        // 1. Sets up a new IoC container
        // 2. Registers all components specified in web.config
        // 3. Registers all controller types as components
        public WindsorControllerFactory()
        {
            // Instantiate a container, taking configuration from web.config
            container = new WindsorContainer(
            new XmlInterpreter(new ConfigResource("castle"))
            );
            // Also register all the controller types as transient
            var controllerTypes =
                from t in Assembly.GetExecutingAssembly().GetTypes()
                                  where typeof(IController).IsAssignableFrom(t)
                                  select t;
            foreach (Type t in controllerTypes)
                container.AddComponentWithLifestyle
                    (t.FullName, t,LifestyleType.Transient);
        }

        // Constructs the controller instance needed to service each request this part is Updated to be compatible with MVC 2
        protected override IController
            GetControllerInstance
            (RequestContext requestContext, Type controllerType)
        {
            return (IController)container.Resolve(controllerType);
        }
        /*
         * For MVC 1 use this
        protected override IController GetControllerInstance(Type controllerType)
        {
            return (IController)container.Resolve(controllerType);
        }*/
    }
}

Note : This post works with Castle 1 RC 3. I recently got an email from one of readers that this not works with the latest version which is 2
so for those folks who want to work which the latest version I notify that instead of AddComponentWithLifestyle method they should use the new AddComponentLifeStyle method.

3.To ASP.NET MVC use your new controller factory add this to the application start method of your global.asax.cs file :

ControllerBuilder.Current.SetControllerFactory(new WindsorControllerFactory());

4. Next we need manipulate our Web.config file in the root of the application: Add a <castle> node directly in the configuration node: <castle><components></components></castle> we edit this shortly. In the configSections node add this:

<section name="castle" type="Castle.Windsor.Configuration.AppDomain.CastleSectionHandler,Castle.Windsor" />

5. To work with our new IoC structure you need to construct your application to use it so follow these steps to set up a simple application which use our IoC implementation:
Create an IEbookRepository interface in Model folder:

namespace Mvc2Application6.Models

{

public interface IEbookRepository

{

IEnumerable<Book> ListEbook();

}

}

As you see it’s a simple interface with a property that returns a list of Books. Book is a simple class with 3 properties:

namespace Mvc2Application6.Models

{

public class Book

{

public int ID { get; set; }

public string Name { get; set; }

public string Author { get; set; }

}

}

Create a concrete class which implements IEbookRepository interface (for simplicity we don’t touch DB and an in memory  list of books satisfies our example):

namespace Mvc2Application6.Models

{

public class EBookRepository : IEbookRepository

{

public IEnumerable<Book> ListEbook()

{

List<Book> books = new List<Book>();

books.Add(new Book { ID = 1, Author = "Steven Sanderson", Name = "Pro ASP.NET MVC framewok" });

books.Add(new Book { ID = 2, Author = "Stphan Waler", Name = "ASP.NET MVC framework Unleashed" });

books.Add(new Book { ID = 3, Author = "Scott Guthrie", Name = "ASP.NET MVC 1.0" });

return books;

}

}

}

Add a new Constructor to your Home Controller:

private IEbookRepository _repository ;

public HomeController(IEbookRepository repository)

{

this._repository = repository;

}

Now we need to tell WindsorContainer to inject IEbookRepository with an object of type EBookRepository so back to your Web.config file and edit castle node we created in step 4:

<castle>

<components>

<component id="EbookRepository"

service="Mvc2Application6.Models.IEbookRepository,Mvc2Application6"

type="Mvc2Application6.Models.EBookRepository,Mvc2Application6"

lifestyle="PerWebRequest">

</component>

</components>

</castle>

This says whenever a class has a dependency to a IEbookRepository (in our example through its constructor) IoC container should load an EBookRepository  object with whenever a web  request comes.

Then we need to register Windsor’s PerRequestLifestyle module in httpModules section :

<add name="PerRequestLifestyle" type="Castle.MicroKernel.Lifestyle.PerWebRequestLifestyleModule,Castle.MicroKernel" />

To register Windsor’s PerRequestLifestyle for IIS 7 refer to the original book “APRESS Pro ASP.NET MVC framework” or use the Google book link above.

So that’s it we set up an IoC container for our ASP.NET MVC application.

you can download sample project here.

Summary: We used Castle Windsor to Set up IoC in a very simple MVC application and for this we created a custom controller factory and added some configuration in web.config file. We also edited Application Start Method to tell MVC use our new controller factory instead of DefaultControllerFactory.